Anycast IPv6 addresses allow the closest resource to respond


We can broadly categorize traffic in four ways:

  • Broadcast – Where traffic goes to all devices
  • Unicast – Where traffic goes to one specific device
  • Multicast – Where traffic goes to several devices that ‘opt in’
  • And, Anycast

Anycast is a feature of IPv6, as well as some other technologies. Multiple devices can be configured with the same anycast address. This is in addition to any other address they may have.

As an example, think of a group of web servers. They each have their own unique global unicast address and a link-local address. Additionally, they share the same anycast address.

When a client wants to access a service on these servers, it can target the anycast address. Any of the servers configured with this address can respond to this request.

The advantage to this is really seen when devices are spread across different sites. A user can move offices regularly and still access the same resources. Because of the anycast IP, the closest device will respond.